A study of the degree of water elimination from ions derived from spirostan-3-ols by electron bombardment has shown that the loss is greatest from those ions produced by the 5 beta-spirostan-3 alpha-ols, less from the 5 beta-spirostan-3 beta-ols and the 5 alpha-spirostan-3 alpha-ols, which give losses of the same order of magnitude; and least from the 5 alpha-spirostan-3 beta-ols. The extent of water elimination can be used to help characterise spirostan-3-ols isolated from plant materials.